A third lane on the Richmond Bridge is just a bandage

The push for a third lane to Richmond has sucked a lot of the air out of the conversation over Central Marin traffic. Cut-through drivers from San Francisco to Richmond are taking up all the space in Larkspur and causing horrific traffic. Thanks to induced demand, however, the third lane will likely fill up soon after it opens and we’ll be back to the same old story.

The most common way to think of traffic is as a gas that fills the space it’s given. No matter how much you build, there will always be traffic to fill it. This couldn’t be more apt for the situation faced by the Richmond Bridge.

Right now, for cut-through San Francisco-to-East Bay commuters, the Marin route is the fastest and cheapest way to get home. These drivers may have to deal with congestion and delays on Sir Francis Drake and 580, but it’s less than what they’d have to deal with on 80 and the Bay Bridge.

If we solve the problem and open a new lane on the Bridge, we’d reduce congestion in Marin enough that we could declare victory… until more people saw that it was a less-congested route than 80 and the Bay Bridge and switched. Either this area will return to its present levels of congestion, or the congestion will migrate to another bottleneck further south in the system, or some measure of both.

This is a much larger version of a problem faced by Los Angeles suburbs, where cut-through drivers, guided by their GPS, take surface streets to escape congestion on freeways. Delays become as bad on surface streets as on the freeway.

If congestion returns to Larkspur Landing, then the widening will simply buy us a few years of peace. If it causes another bottleneck, we’ll have bought some peace to Larkspur Landing at the cost of congestion elsewhere. If it’s both, then nobody wins.

Longer-term solutions depend on which outcome occurs; let’s look at each in turn.

Congestion comes back to Larkspur Landing only

If this occurs, the only real solution is to keep traffic on the freeway as long as possible by installing a proper 101-580 interchange in San Rafael. This interchange has been proposed before, but community opposition to a towering flyover connecting westbound 580 with southbound 101 scuttled the project. If the same opposition arises again, it might be worthwhile to simply remove that aspect and only do the eastbound 580 to northbound 101 aspect.

For now, at least, Caltrans ought to remove signs at the Sir Francis Drake Boulevard exit indicating that that is the way to 580.

Congestion occurs elsewhere in the system

The most likely location for congestion to occur is south of Marin City: on the Waldo Grade, Golden Gate Bridge, Lombard, or Van Ness, all of which are good targets for transit. Both Marin commute trips and local San Francisco trips are relatively easily served by transit. The upcoming Van Ness BRT line will make a big difference to that corridor, and an extension onto Lombard would help both GGT and Muni riders. Extending the HOV lanes onto the Waldo Grade by converting one of the through-lanes would speed transit and encourage carpooling, also helping alleviate congestion.

Alas, transit sometimes functions like adding more lanes: the amount of congestion stays constant even while the transportation capacity of a road to move people increases. At least we can comfort ourselves that fewer people will experience congestion from behind the wheel.

Congestion occurs both at Larkspur Landing and elsewhere

If this occurs, then planners will need to employ both solutions: add the interchange and improve transit.

The only permanent solution

The rub, of course, is that congestion is ultimately not a solvable problem without an economic downturn. Houston, Seattle, Los Angeles – all have tried to fix congestion by increasing roadway capacity, and none have succeeded. Anthony Downs, in his 1992 book Stuck in Traffic, said that widening a freeway doesn’t work thanks to what he called a “triple convergence”:

In response, three types of convergence occur on the improved expressway: (1) many drivers who formerly used alternative routes during peak hours switch to the improved expressway (spatial convergence); (2) many drivers who formerly traveled just before or after the peak hours start traveling during those hours (time convergence); and (3) some commuters who used to take public transportation during peak hours now switch to driving, since it has become faster (modal convergence).

The only way out is to view road space like a resource, and to price it as such. Jarrett Walker describes it thus:

Fundamentally, congestion is the result of underpricing. If you give away 500 free concert tickets to the first 500 people in line, you’ll get 500 people standing in line, some of them overnight. These people are paying time to save money. Current prevailing road pricing policy requires all motorists to act like these frugal concertgoers. Motorists are required to pay for road use in time, rather than in money, even though some would rather do the opposite and our cities would be safer and more efficient if they could. Current road pricing policy requires motorists to save money, a renewable resource, by expending time, the least renewable resource of all.

For the Bay Area, this would mean varying bridge tolls during the day so that congestion never builds up. Downs’ triple convergence would work in reverse.

With a rush hour 80 and Bay Bridge free of congestion, cut-through travel would be much less attractive for Contra Costa commuters. Those that still made the journey would likely not be enough to congest 101 at all.